The VAV-TROL™ variable air volume is a product of M&I's extensive research and development efforts that kept M&I at the forefront in the field of HVAC design. It adjusts the blade loading for VAV systems, thus effectively varying the flow rate down to shut-off.

VAV-TROL™ is an efficient and economical alternative to inlet vanes as well as inverter speed controls. VAV-TROL™ is also far superior to other volume control devices currently in the market which use volume control disks / cones at the fan inlet with support structures and actuators mounted in the airstream. These, components would cause turbulence at the fan wheel intake resulting in noise generation (up to 10 dB) and energy loss (up to 10%).
WHISPER-AIR uses an extended acoustical inlet flow concentrator with a large lip radius at the entry into the fan wheel. There are no components in the airstream disturbing the flow pattern entering the fan. The inlet lip is constructed of heavy gauge spun sheetmetal and is carefully matched to the fan wheel.

With the VAV-TROL™ system, the complete fan assembly c/w motor, vibration isolators, etc. is mounted on four rugged, low friction casters operating on two guide rails, and can be moved with a small pneumatic or electric operator. The VAV-TROL™ System moves the fan wheel over the inlet flow concentrator toward the inlet side, reducing the working width of the fan wheel, and thus, reducing the airflow rate and the horsepower, while the fan speed is kept constant. The airflow rate can be reduced from 100% to as low as 10% while meeting the static pressure requirements of the system and without stalling the fan. Complete shut-off can also be provided. Furthermore, the benefits offered by the WHISPER-AIR unit are maintained at all airflow rates.

VAV-TROL™ provides quiet, efficient and reliable operation. Only a small operator (pneumatic or electric) is required to provide the volume control. The system can be designed to fail at minimum or maximum position, as required. No complex mechanisms or large actuators are needed which makes it a simple, economical and reliable operation that delivers the required fan performance.

A volume measuring device, using multiple pressure sensors located at the fan inlet flow concentrator, can be incorporated into the VAV-TROL™ device.